Civil Engineering Infrastructures Journal
Volume:47 Issue: 2, Dec 2014

In the last two decades, there has been an increasing interest in structural engineering control methods. Shape memory alloys and seismic isolation systems are examples of passive control systems that use of any one alone, effectively improve the seismic performance of the structure. Characteristics such as large strain range without any residual deformation, high damping capacity, excellent re-centering, high resistance to fatigue and corrosion and durability have made shape memory alloy an effective damping device or part of base isolators. A unique characteristic of shape memory alloys is in recovering residual deformations even after strong ground excitations. Seismic isolation is a device to lessen earthquake damage prospects. In the latest research studies, shape memory alloy is utilized in combination with seismic isolation system and their results indicate the effectiveness of the application of them to control the response of the structures. This paper reviews the findings of research studies on base isolation system implemented in the building and/or bridge structures by including the unique behavior of shape memory alloys. This study includes the primary information about the characteristic of the isolation system as well as the shape memory material. The efficiency and feasibility of the two mechanisms are also presented by few cases in point.

Corrosion of steel reinforcement is one of the most prevalent causes of reinforced concrete (RC) structures deterioration in chloride-contaminated environments. As a result, evaluating the impact of any possible corrosion-induced damages to reinforced concrete bridges strongly affects management decisions: such as inspection, maintenance and repair actions. The corrosion propagation phase is a significant factor in the service life of reinforced concrete structures and thus, it is requires appropriate attention. Various models have been developed to simulate and/or predict the propagation phase. This paper proposes that a method in which a reliability framework is developed to assess the durability of reinforced concrete structures under corrosion inmarine environments functions better. The main concern of this study is chloride-induced corrosions.In due regard, serviceability and ultimate limit states of the structure are also taken into account. Subsequently, the proposed method is employed to review the existing models for prediction of corrosion propagation.

Withdrawal of oil and gas from reservoirs causes a decrease in pore pressure and an increase in effective stress which results to a reservoir compaction. Reservoir compaction will result in surface subsidence through the elastic response of the subsurface. Usually in order to determine the subsidence above a hydrocarbon field, the reservoir compaction must be first calculated and then the effect of this compaction on the surface should be modeled. The use of the uniaxial compaction theory is more prevalent and an accepted method for determining the amount of reservoir compaction. But despite of the reservoir compaction calculation method, there are many methods with different advantages and shortcomings for modeling of surface subsidence. In this study, a simple analytical method and semi -analytical methods (AEsubs software) were used for modeling of the surface subsidence of the South Pars gas field at the end of the production period.

Naturally occurred soil deposits inherit heterogeneity and anisotropy in their strength properties. The main purpose of this paper is to model the soil stratum with anisotropy consideration and spatially varying undrained shear strength by using random field theory coupled with finite difference numerical analysis to evaluate their effect on the bearing capacity of the shallow foundations. In the present study, undrained shear strength of soil is considered as a stochastic variable and is assumed to be log-normally distributed and spatially correlated throughout the domain. Two kinds of anisotropy of cohesion are incorporated in the analyses. As the first kind, mechanical anisotropy of cohesion was taken into account by generalizing the conventional isotropic Mohr-Coulomb failure criterion to the anisotropic one, and the second kind is the heterogeneity anisotropy associated with difference in the correlation structure of the cohesion data in the horizontal and vertical directions considered by a special anisotropic correlation function. The results showed the importance of different components of anisotropy and the stochastic variation of shear strength parameters. Mechanical anisotropy and the spatial variability of the cohesion showed that they have significant effects on the bearing capacity of the shallow foundations and their negligence will lead to an under-conservatism.

Numerous techniques have been presented by different researchers to analyze piled raft. In order to analyze pile foundation, soil can be modeled as spring, continuous medium, or porous media. Pile can also be modeled as spring or continuous medium. This study includes three main stages: a short description of different types of analysis methods of pile foundation, writing a computer program based on the finite element method (FEM) for analyzing piled raft foundation (in this program, foundation is modeled as a flexible plate, soil and pile are modeled by Winkler springs), and comparison of different concepts of pile group design.

Fiber reinforced concrete (FRC) has been widely used due to its advantages over plain concrete such as high energy absorption, post cracking behaviour, flexural and impact strength and arresting shrinkage cracks. But there is a weak zone between fibers and paste in fiber reinforced concretes and this weak zone is full of porosity, especially in hybrid fiber reinforced concretes. So it is necessary to apply a material that reduces porosity and consolidates this transition zone. In this research first, the flexural and impact resistance tests were carried out on hybrid fiber reinforced concretes to choose the optimum percentage of steel and polypropylene fibers based on flexural toughness, modulus of rupture and impact resistance. Finally, compressive strength tests were conducted on selected hybrid fiber reinforced concretes containing pumice and metakaolin to choose the better pozzolan and replacement level based on compressive strength test. Results showed that, metakaolin with 15% substitution for cement had a significant role in increasing compressive strength. However, pumice did not act on the same basis.

In this paper, the grouting ability of sandy soils is investigated by artificial neural networks based on the results of chemical grout injection tests. In order to evaluate the soil grouting potential, experimental samples were prepared and then injected. The sand samples with three different particle sizes (medium, fine, and silty) and three relative densities (%30, %50, and %90) were injected with the sodium silicate grout with three different concentrations (water to sodium silicate ratio of 0.33, 1, and 2). A multi-layer Perceptron type of the artificial neural network was trained and tested using the results of 138 experimental tests. The multi-layer Perceptron included one input layer, two hidden layers and one output layer. The input parameters consisted of initial relative densities of grouted samples, the average size of particles (D50), the ratio of the grout water to sodium silicate and the grout pressure. The output parameter was the grout injection radius. The results of the experimental tests showed that the radius of grout injection is a complicated function of the mentioned parameters. In addition, the results of the trained artificial neural network showed to be reasonably consistent with the experimental results.

Some considerable damage to steel structures during the Hyogo-ken Nanbu Earthquake occurred. Among them, many exposed-type column bases failed in several consistent patterns, such as brittle base plate fracture, excessive bolt elongation, unexpected early bolt failure, and inferior construction work, etc. The lessons from these phenomena led to the need for improved understanding of column base behavior. Joint behavior must be modeled when analyzing semi-rigid frames, which is associated with a mathematical model of the moment–rotation curve. The most accurate model uses continuous nonlinear functions. This article presents three areas of steel joint research: (1) analysis methods of semi-rigid joints; (2) prediction methods for the mechanical behavior of joints; (3) mathematical representations of the moment–rotation curve. In the current study, a new exponential model to depict the moment–rotation relationship of column base connection is proposed. The proposed nonlinear model represents an approach to the prediction of M–θ curves, taking into account the possible failure modes and the deformation characteristics of the connection elements. The new model has three physical parameters, along with two curve-fitted factors. These physical parameters are generated from dimensional details of the connection, as well as the material properties. The M–θ curves obtained by the model are compared with published connection tests and 3D FEM research. The proposed mathematical model adequately comes close to characterizing M–θ behavior through the full range of loading/rotations. As a result, modeling of column base connections using the proposed mathematical model can give crucial beforehand information, and overcome the disadvantages of time consuming workmanship and cost of experimental studies.

Torsion of many symmetric structures, which were designed based on the seismic codes, is due to their asymmetricity induced during inelastic behavior. Although the structure was designed symmetrically assuming elastic based criteria, different factors such as material inconsistency in structure, construction details discrepancy and construction errors may result in asymmetric behavior in inelastic deformation range. So far, these considerations have been rarely contemplated in previous published investigations and should be studied regarding the importance of irregularity in increase of seismic demand of structures in the inelastic range. In this paper, as the first step, the asymmetry and irregularity in plan due to non-similar inelastic characteristics with respect to axis passing through center of gravity as well as the effect and importance of each irregularity factors are studied by changing the excitation properties applying to one-storey one-bay steel structures. This simplified structure is chosen due to studying and illustrating the absolute effect of this kind of irregularity in which higher mode effect is eliminated. The results show that the behavior of a structure with inelastic asymmetry is completely different from the structure with elastic asymmetry. As for inelastic asymmetry structure, although the translational and rotational oscillations before yielding were uncouple, these DOFs after yielding become coupled until reaching the terminal rotation point (rotation reaches a constant value) and then become uncoupled, i.e., again oscillated symmetrically. This behavior is different from the structures with elastic asymmetricity, in which the translational and rotational movements being coupled during all the excitation time. This effect has not been recognized in previews studies on inelastic behavior of initially elastic symmetry buildings. The study of these behaviors aids the designer to choose the appropriate rehabilitation method for a vulnerable irregular structure.

Reactive Powder Concrete (RPC) is an ultra high performance concrete which has superior mechanical and physical properties. The RPC is composed of cement and very fine powders such as crushed quartz (100–600 μm) and silica fume with very low water/binder ratio (W/B) (less than 0.20) and Super Plasticizer (SP). The RPC has a very high compressive and tensile strength with better durability properties than current high performance concretes. Application of very low water/binder ratio with a high dosage of super plasticizer, different heat curing processes and pre-setting pressure improve mechanical and physical properties of RPC. In this study, the RPC is composed of available materials in Iran. Two different mixing proportions, different water/binder ratios for preparation of samples, different super plasticizer dosages, five different (0, 25, 50, 100 and 150 MPa) pre-setting pressure and 7 different curing regimes were used in samples preparation and experiments. Results showed that appropriate water/binder ratio and super plasticizer dosage, higher temperature and pre-setting pressure increase the workability, density and compressive strength of compositions.